It is the purpose of this project to identify and characterize a possible factor in the vitreous of patients with diabetic retinopathy and related eye disorders, which is responsible for the development of abnormal vascular proliferation. Diseased human vitreous is removed from the eyes of patients undergoing pars plana vitrectomy for indicated surgical ocular disease. This material is then concentrated, purified, and evaluated for vasoproliferative activity. Bioassay systems, as well as tissue culture techniques, are utilized in the identification of physiologically active substances which produce neovascularization. Further biochemical characterization of the responsible vitreous factor will be performed as vasoproliferative activity is identified.